1. Field of the Invention
The present invention relates to a technology for recovering data stored in a storage device from which a failure is detected from among storage devices constituting a disk array.
2. Description of the Related Art
In a redundant-arrays-of-independent-disks (RAID) structure that includes a plurality of disk devices, when a failure occurs in a disk device, a reconstruction processing is generally performed for recovering data stored in the disk device.
With the reconstruction processing, the data stored in the failed disk device is recovered by performing an exclusive-OR operation between data and parity read from the rest of the disk devices in the same RAID structure.
The recovered data is to be stored in a disk device prepared as a spare disk device that is provided separately from the rest of the disk devices. At this moment, if the capacity of the failed disk device is smaller than the capacity of the spare disk device, a free space is to be left without being used in the spare disk device.
A technology for removing such a free space is disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-149374. According to the technology, when data with a specific size needs to be stored in a disk device, a logical storage area with a required size for storing the data is formed by combining the disk devices, and the data is stored in the logical storage area.
Further, Japanese Patent Application Laid-Open No. H6-230903 and Japanese Patent Application Laid-Open No. 2000-200157 disclose technologies, in which recovered data is stored in free spaces left in each of the disk devices in which data is already stored, in a striping manner, instead of separately preparing a spare disk device.
However, with the disclosed technologies, there still is a problem that it takes a longer processing time for performing the reconstruction processing when a communication speed of transmitting the data on a communication path to a destination disk device is slow.
For example, a RAID structure using a fiber channel-arbitrated loop (FC-AL) technology includes a configuration in which a plurality of groups including the disk devices connected in a loop via a fiber channel are formed. With the above configuration, if a disk device connected to a fiber channel with a large communication load is selected as a data recovery destination for performing the reconstruction processing, a high speed can hardly be achieved in performing the reconstruction processing.
Further, when the disk devices are connected to switches while groups including the disk devices and the switches are formed in the above configuration, and when a disk device connected to a switch with a large communication load is selected as the data recovery destination for performing the reconstruction processing, it is also difficult to perform the reconstruction processing at a high speed. Moreover, if the operation speed of the disk device is slow, the reconstruction processing cannot be performed at a high speed.
Because the RAID structure becomes in a degeneration state during a performance of the reconstruction processing and redundancy of the data in the RAID structure is not to be assured, it is required to complete the reconstruction processing as fast as possible. Therefore, it is critical to select a proper disk device as the data recovery destination and perform the reconstruction processing at a high speed.